1. Field of the Invention
This invention relates to differential gears having a differential motion limiting function.
2. Description of the Related Art
Among automobile differential gears, those (called limited slip differentials) having a differential motion limiting function, and fashioned so that, when the wheel on one side only tries to freewheel, adequate turning force is still transmitted to the wheel on the other side through clutch means, are widely employed in order to prevent the loss of adequate turning force to the wheel on one side when the wheel on the other side freewheels because it is on ice, snow, or mud or the like, and to prevent the auto-body fishtailing phenomenon when executing a turn or quick getaway or the like.
The differential gears 100 diagrammed in FIG. 14, for example, are described in Japanese Patent Publication No. S55-27980/1980 (published) and in Japanese Patent Application Laid-Open No. S58-221046/1983 (published). These differential gears 100 comprise a pair of pressure rings 103 deployed inside a differential case 101 so as to freely move in the direction of wheel axles 102 but be incapable of relative turning, a pinion shaft 104 deployed perpendicularly to the wheel axles 102 in a condition wherein the shaft end is held between the pressure rings 103, a pinion gear 105 deployed so as to freely turn on the pinion shaft 104, a pair of side gears 106 deployed to the left and right wheel axles 102, respectively, so as to be incapable of relative turning, which side gears 106 sandwich the pinion gear 105 and mesh with the pinion gear 105 on either side thereof, actuation means 108 that, in response to increases in relative turning torque between the pinion shaft 104 and the differential case 101 during differential motion, activate the pressure rings 103 in a direction such that the clearance 107 between the pressure rings 103 becomes greater, and clutch means 109 deployed on both sides of the pair of pressure rings 103 in the wheel axle direction, which clutch means 109 limit the differential motion of the left and right wheel axles 102 as the clearance 107 actuated by the pressure rings 103 becomes larger.
For the actuation means 108, various shapes are proposed. In one example thereof which is adopted, a cam unit 110 having a square shape one diagonal whereof is set in the wheel axle direction is formed on one shaft end of the pinion shaft 104, and a substantially V-shaped cam channel 111 into which the cam unit 110 engages is formed in the pressure rings 103.
In the differential gears 100, moreover, when relative turning torque occurs between the pinion shaft 104 and the differential case 101, the clearance 107 between the pressure rings 103 will widen due to the actuation means 108, and, thereby, the clutch means 109 will be activated and the differential motion of the left and right wheels will be limited, but the configuration is made so that, in order that the clearance 107 between the two pressure rings 103 will return to a set interval at normal times, elastic members 112 such as plate springs are positioned outside of the two sets of clutch means 109 in the wheel axle direction, so that the pressure rings 103 are urged in a direction such that they approach each other through a plurality of clutch plates 113 of the clutch means 109.
Now, in differential gears 100 such as this, it is necessary to secure sufficient area in the friction pressing portion of the clutch plates 113 in order that the differential motion of the left and right wheels will be definitely limited by the clutch means 109 in a differential motion limiting condition. However, the size of the differential case 101 is restricted by the positional relationship between the differential gears 100 and various equipment on the automobile side, making it very difficult to establish that size larger than what it is currently. For that reason, it has been virtually impossible to obtain a more adequate differential motion limiting action than what is obtained currently by increasing the number of clutch plates 113 or making their size larger.
In a horizontal engine vehicle, in particular, as compared to an inline engine vehicle, more severe restrictions are imposed by the layout of the engine and the parts peripheral thereto, and the shape and capacity of the differential case are sharply restricted. As in the differential gears 120 diagrammed in FIG. 15, for example, it is necessary to diminish the diameter of the left portion of the differential case 121, making it very difficult to establish satisfactorily large area in the friction pressing portion of the clutch means 122. In addition, when the urging force of the elastic members 123 is increased in order to increase the friction pressing force, it becomes impossible to obtain a differential motion condition while effecting a slow turn, as described earlier, wherefore it has been impossible to obtain adequate differential motion limiting action.
The applicant, as a result of assiduous investigations into how to adequately secure friction pressure force in clutch plates, discovered that, whereas configuring the clutch means deployed on either side of the two pressure rings in the wheel axle direction in left-right symmetry was established as one design condition in conventional differential gears, the same kind of differential motion limiting action could be obtained even with one member of the clutch means omitted. Thereupon, the applicant proposed differential gears such as the differential gears 120A diagrammed in FIG. 16, wherein clutch means 122A are only deployed between the left portion of a differential case 121A having room to spare and the wheel axle 102 on the left side.
However, even in these differential gears 120A, a problem developed in that, depending on the shape of the differential case 121A, with a differential case 121B wherein the right portion is given a large diameter, as indicated by the imaginary lines in FIG. 16, for example, a comparatively large portion of wasted material is formed in the right portion of the differential case 121B. Besides that, moreover, in the differential gears 100, 120, and 120A described in the foregoing, a side wall 103a is formed which extends to the vicinity of the sleeves of the side gears 106 in the pressure rings 103 in order to catch substantially the entire side surface of the clutch plates 113, but the applicant discovered that the number of clutch plates 113 becomes fewer precisely by the measure of the thickness t of the side wall 103a, and that there still exists ample leeway for enhancing the friction pressure force of the clutch plates 113.
In differential gears such as described above, moreover, it is desirable that, fundamentally, a differential motion condition ensue wherewith maneuvering in tight places can be done when making low-speed turns such as when garaging a vehicle or parallel parking, and that, when one wheel is freewheeling, or a quick getaway is being made, or when turning at high speed or under heavy loading, a differential motion limiting condition ensue wherewith stable initial performance is obtained.
With conventional differential gears, however, as seen in the differential gears 100, for example, given the relationship whereby the left and right pressure rings 103 are urged by elastic members 112 in a direction such that they will approach each other, via the clutch plates 113, when the urging force is set to be weak, manipulating the clutch means 109 by the actuation means 108 becomes easy, whereupon there are cases where a differential motion limiting condition will ensue even when making a low-speed turn, and the differential motion condition will not stabilize, whereas, when the urging force is made strong, the actuation means 108 reach a condition where differential motion is possible, but, due to the urging force of the elastic members 112, the clutch plates 113 are normally friction pressed, and attain a substantially differential motion limiting condition, as a consequence whereof a differential motion condition cannot after all be stably secured during low-speed turning. In other words, problems arise in that either the ability to maneuver in tight places during low-speed turning suffers, or the so-called chattering phenomenon occurs wherewith the differential motion limiting condition and differential motion condition switch back and forth, controllability deteriorates, and the differential gears 100 and equipment peripheral thereto are adversely affected by shocks during chattering.
For this reason, setting the urging force is very difficult. In a competition vehicle wherewith sport driving is presupposed, for example, what is currently done is that controllability during low-speed turns is to some extent sacrificed, and the urging force of the elastic members 112 is set on the high side in a configuration wherewith an adequate differential motion limiting condition can be realized at high speed or under heavy loading.